#include <iostream>
#include <vector>

int_least64_t search(int n, std::vector<int_least64_t>& cache) {
	if (n == 0) return 1;
	if (n == 1) return 1;
	int_least64_t ret = cache[n - 1];
	if (ret >= 0) return ret;

	ret = search(n - 2, cache) + search(n - 1, cache);
	cache[n - 1] = ret;
	return ret;
}

int main()
{
	int n;
	std::cin >> n;

	std::vector<int_least64_t> cache(n, -1);
	int_least64_t result = search(n, cache);

	std::cout << result << std::endl;

	return 0;
}